Amperage output is entirely unconnected with voltage output, assuming the regulator is functioning correctly (overcharge is overcharge by any measure). Just get the manufacturer to confirm max voltage output is 14.4v. You can get 28 amp alternators and 200+ amp alternators and they all run 14.4v.

Be aware that some instruments are meant to be run at a lower than system voltage through an IVS (normally 10v or so). Running them at full system voltage will do a lot more damage than running them a volt or so over 14.4v. Plenty of OE choices, you don't need nuthin' fancy.

"If an honest man is wrong, after demonstrating that he is wrong, he either stops being wrong or he stops being honest." Anon

I noticed someone on some other forum somewhere trying to sell "permanent magnet" alternators.

Such things have been used for a long time as wind generators on boats.
Understanding them is a step in the right direction.
Often they're 24v but they don't actually have a voltage because they're a "current pump".
The stronger the wind is, the more current it pumps into your battery. There's no voltage regulation, it just pumps current.
In order for the current to flow into the battery, the voltage needs to be higher.

Think of it as being a bit like an EFI fuel pump and a regulator. The pump provides the flow in the return line back to the tank so long as it can overcome the regulator.That maintains constant pressure in the fuel rail.

The downside of a permanent magnet alternator......no regulation.........in a storm you fry the batteries due to too much current/voltage. So in a storm the normal approach is to increase electrical load to keep the volts down or to flick a switch to put the power into a dummy load. Increasing the load also slows it down by causing drag so it won't fly apart.

With a normal alternator, the regulator shuts down the current in the rotor which reduces the output.
If the output voltage is too high, it's a dud regulator and you'll kill the battery as well as other things. I just used the V1 as a good example because they fail first. They're expensive too.

PM automotive alternator rotors, either external or internal, have been around since the birth of the silicon diode. Mostly on motorcycles and smaller stationary engines, for one simple reason, they are cheap and uncomplicated, although the also package well. Doesn't mean they are any good. Depending on how they are controlled they can be very inefficient, relatively, ask anyone with, say, an old Triumph cycle with a big finned heatsink under the headlight housing a fat Zenner. The modern three phase crank end ones are a reasonable compromise.

PMs on wind turbines are a different kettle of fish, as the smaller ones mostly run into inverters and are tolerant of tolerably wide voltage outputs.

"If an honest man is wrong, after demonstrating that he is wrong, he either stops being wrong or he stops being honest." Anon

OK, so how are the stock ones rated at whatever amps? If you don't know that then you don't know how the upgraded ones are rated either.

Long time ago I noticed that replacement alternators had different Amp 'rating' than spec'd in the Chrysler factory service manuals. The ratings seemed to be in-line with the load testing that could be done in car. More recently I've noticed that replacement GM (Delco) SI alternators generally have a similar or same ampere rating to the OEM. These seem to be approximate maximum output but at least with the later AMC service manuals, there is no load test procedure for troubleshooting.

Alternator output is mostly rated 'hot' (90degC springs to mind as a common value but I'd have to look it up, and it will vary by manufacturer). Again ultimate output is secondary to the output curve, which most manufacturers will supply.

Maybe that temperature difference explains why this old test tag for a remanufactured 94 Amp 12SI shows more than 94 Amps?

Found in box with reman 7294. May ore may not have been for the specific alternator in the box.

In contrast, the report from the parts store's own test machine at these is a little baffling to me. There's no obvious load test. Ripple volts I understand, I'm guessing that's how the machine passes the diodes, if anyone can explain the rest I'd appreciate it.

All above are allowed plus minus 3 Amps for temperature variation.
Current Output above is measured at the alternator with the engine at 1250 RPM and 15 Volts. If current is measured at Battery, output is expected to be approximately 5 Amps less. Voltage is controlled by a variable load (carbon pile) across the battery. The outputs are not the maximum current.

So with here's an example when the factory spec and the parts store rating will not match.

Nothing ever matches when it comes to electricity and cars.
Output goes up with RPMs.
If you want to trick someone with numbers, just spin it quicker or lower the voltage of the load that you're driving.

The output diodes have a certain current rating which shouldn't be exceeded.
If you upgrade them, does it make your alternator have more output?
No, of course not.
But if you spin it quicker and turn up the voltage at the regulator, it'll work a bit harder, you might get more out of it.

The regulator, all it does is gives full voltage/current to the rotor at low speed. As the output voltage rises with RPMs, that gets sensed which reduces the current/voltage to the rotor to level off the output voltage.

Yes. We've established that marketing can fool people. My first and second post was to provide some specific examples of how rating methods can vary. At the same time I am implicitly asking if people have additional examples that can help fill in the blanks. At the bottom of the first post, I also raised questions about how and what some of the chain parts store's alternator test machine's do.

There's really no mystery about how to compare; and IF one can find the current output specs the variables can be duplicated. I provided an actual performance curve for a '94 Amp' 12SI above. AC Delco provides performance curves for their alternators (uh generators as they prefer to say :LOL:) Type in whatever model you are looking for here
For example here's the curve they publish for the 3 12SI outputs including the 94 Amp

While I haven't found anything similar for the early Essex/Chrysler alternators, here is a scan from a later shop manual (late '70s or early 80s?) that does give both the alternator rating as well as the test output current.

I've been thinking about rigging up a test station just for fun to test the stack of alternators I've collected. It wouldn't take that much (other than precious space). A spare battery, carbon pile and ammeter, voltmeter and an electric motor with a V belt pullery. Well really needs to be a motor with a speed control. The major variables are controllable with the rheostat for load and the rpms with the motor also with a rheostat or pulley sizes. Actually will also need a way to measure the rpms if using a variable speed motor.

Just curious ... some vendors, (like above), will offer a single wire a 10SI or 12SI alternator which will produce in excess of 100 amps of current.
AND, when using a large pulley does not the cooling capacity also suffer...?

I think the question at the beginning here was ... are these claims accurate and if they are, can these alternators be used continuously...?

I would say they should only be used in NON-continuous situations if those amp ratings are realistic.

Walter R. Malik wrote:Just curious ... some vendors, (like above), will offer a single wire a 10SI or 12SI alternator which will produce in excess of 100 amps of current.
AND, when using a large pulley does not the cooling capacity also suffer...?

I think the question at the beginning here was ... are these claims accurate and if they are, can these alternators be used continuously...?

I would say they should only be used in NON-continuous situations if those amp ratings are realistic.

That would seem to be a safe approach to higher output units.
With your second question or point; it seems we agree it depends on whether the rating method for both the original and the aftermarket vender are known. I realise the Steve (the OP) started this a year ago, but by crowd sourcing and with some help from guys like BC, we *might* be able to get closer to an answer for at least some commonly used models. This why I posted the info I had found on the delco 'generators' and chrysler alternators

FWIW, based on the information i've found on the 'net including AC Delco, the cooling capacity of a 12SI is greater than as 10SI or 15SI. This is due to the fan and intake port sizes. However on all three models these intake ports are located on the back, so will often be drawing exhaust heated air. Also, I tend to give some weight to factory engineering and design decisions. The 12SI eventually was available from Remy-Delco with a 94 Amp rating. For AMC/Jeep this option was available starting in '87. Before that, fleet trucks had the option of an 85 Amp alternator, but this turns out to been a 15 SI. This suggests to me that there's probably a reason not to 'upgrade' even a 10SI to even 85 Amps, but a 94 AMp 12 SI should be fine even for long duty cycles at higher output. Also note that if you download the 10SI performance graphs from ACDelco, the higher output alternators have peakier performance. That's pretty much in line with BC Jonny's comment a few posts back.

Whether it is 1 wire or 3 to the alternator doesn't seem to matter as far as output goes.

For the Essex and Chrysler units through '72, I haven't really found the sort of info I found for the 10 and 12Si Delcos. I'm additionally curious about whether their perfomance is related to whether B type regulation is superior to A type regulation, and whether a points regulator for any reason would be a limiting factor. I don't see the latter, but do suspect the universal ? change to regulating the ground rather than supply had some rationalle.

Honestly Kevin, the off-roaders I read about discussing these issues are more interested in things like on board air, dual batteries, and using the batteries for emergency arc-welding. I think those needing banks of lights are subset involved in higher speed off-pavement akin to FIA rallies. A lot of FSJeepers who need more current at low rpm will go to the newer CS series, and then some changes to the charging system wiring is also done.

Mattax wrote:I'm additionally curious about whether their perfomance is related to whether B type regulation is superior to A type regulation ......

Matt, as per conversation thought I would post this up here for the benefit of others:

I know it as 'field to positive' and 'field to negative' switching, whether the reg is interposed between the positive feed or negative ground.

Yes I'm aware of the 'one' and 'two' wire Chrysler units.

There is no real advantage to either, it's just mostly manufacturer convenience. Most early units were field to pos, as they often had 'ignition fed' fields. By regulating the feed to the rotor, via the positive brush, and internally earthing the neg brush, no other wiring was need. As alternator fields became machine powered, via the 'field triode', field to neg made more sense.

Most contemporary machines switch 'field to neg'. Some regulators you can chop up the external wiring and wire them either way (convert a 'f to +' to 'f to -') and they work just as well. No magic there, I'm afraid .....

Essentially it ads nothing to output, it's just a control (regulation) decision. Output current, as discussed elsewhere, is built in at the design stage due to conductor gauge/type and stator 'iron' (it's actually steel) saturation.

"If an honest man is wrong, after demonstrating that he is wrong, he either stops being wrong or he stops being honest." Anon

Thank you for clearing that up. Let me add this from our conversation.

Mattax wrote:I can see that making an electromechanical regulator switch off the positive is fairly simple. Was it hard in 1970 to make a solid state equivalent?
It's interesting now that solid state replacement regulators are available for 'single' field wire systems, a number of enthusiasts still feel the need to convert to the 1970 up ground switching arrangement.

BCjohnny wrote:By 1970 no, ss regs '+ sw' regs were commonplace, but manufacturers only change parts often grudgingly. ... As said earlier 'ground switching' is overwhelmingly the most preferred OE method today, so there a economies of scale, and not having to use en application specific reg, in choosing this method. If there are problems '+ switching' a field I'm not aware of it, some manufacturers continued to use it, and alt performance is not affected.

I thought this might be of interest to some who are following this thread:

The 'field trio' or 'triode' (3 pos diodes) is the 'diode trio' and on a 12SI is physically bolted to the 6 diode (3 pos, 3 neg) 'main power rectifier bridge' via the nuts that hold the stator leads (conductors) to it.

The 'diode trio' bleeds current from the stator, normally around 3-4 amps (12v system) to power the 'field' circuit, comprising the rotor/brush/regulator circuit, creating the modulated electro-magnetic field that cuts through the stator windings to create the charging current in the stator conductors. There are only 3 diodes as it just requires a small amount of the positive component of the charging current to power up the field circuit. It could use a 6 diode 'fwrb', but this would be a waste of money and components in this instance.

Once charging the alternator field is self sufficient, not requiring an external feed, apart from the 'remote sense terminal' if fitted to regulate voltage. A 12SI usually has a two terminal reg, 'remote sense' and 'warning lamp', the latter being redundant once charging, unless there's a problem.

The 'main power rectifier bridge' (the extruded finned aluminium heatsink on a 12SI) has 6 diodes as it's a 'fwrb'' that not only rectifies the positive 14v component of the AC (alternating current) wave, but also effectively 'flips' the the negative 14v component of the AC wave thus doubling up the charging current available and creating a smoother DC 'ripple' for better efficiency. The negative component of the wave is therefore utilised, instead of just blocked.

It's easier to understand the last point if you see electricity as 'potential difference' between two points rather than pos and neg per se. The 14v neg component of the AC wave is just as useful as the 14v pos component if 'processed' correctly, which is done through the 'full wave, main rectifier power bridge', with 6 diodes as outlined above.

On most 'machine fed field' older alternators, there are only usually on 9 diodes in total. 6 power, 3 field. Modern alternators tend to be different although quite a few '9 diode' types still exist. Even older types, such as the 10DN, have ign fed fields, so just have six power diodes.

Simplifications excepted, that's about it.

Hope this helps, John.

[fwrb = 'full wave rectifier bridge']

"If an honest man is wrong, after demonstrating that he is wrong, he either stops being wrong or he stops being honest." Anon

Awesome post guys. It is great when someone like me who has almost no knowledge of how alternators really do their work can educate oneself on the actual way in which alternators accomplish charging, are constructed in quite a few different ways and have several different system types! Thank You!

I think one thing that nobody has yet mentioned is that alternators are 3 phase.
With a single phase and full wave rectification, you need 4 diodes.
With 3 phase, you need 6 diodes....so that's where the 6 comes from.

When you rectify 3 phase, the resultant voltage is flat, there's no ripple so there's no filtering required.
The extra 3 (to make 9 in total)....they feed the rotor.
If you've got an alternator that won't start up, or you have to rev it hard to start up or it's got a noisy output, it's usually a failed diode.
Another thing to think about is watts.
That's volts times amps.
If an alternator can make 200A at zero volts...that's zero watts.
Likewise if it can make 300 volts and zero amps , it's also zero watts.
So if you test it at say 12v instead of 14.4 volts it's going to appear to be better than what it really is.
There's lots of trickery out there.

The above example of 94A at 12V.............1128W.
If it's at 14.4V then it will probably only output 1128/14.4 = 78A.....but then it might not.
To know for sure, it'll need measuring.